The present invention generally relates to compressors, and more particularly to a compressor having a starting load reducing apparatus for automatically reducing operational load of a main compressor body which acts on a motor upon starting of the compressor.
Generally, an air compressor is operated when a main compressor body is driven by a motor. The characteristic of the motor is generally such that the torque is small upon starting of the motor. Hence, upon starting of the compressor, it is desirable for the load which is acting on the motor to be small. Thus, conventionally, there was a simple apparatus for reducing the load upon starting of the compressor. In this conventional apparatus, a manipulation knob which is manually manipulated from the outside, is provided on the main compressor body, and this manipulation knob is pushed and manipulated upon starting of the compressor to open a suction valve in the main compressor body. Therefore, in the above conventional apparatus, a compression chamber and an intake chamber are forcibly communicated, so that the main compressor body does not perform a compressing operation, that is, performs a non-compressing operation, upon starting of the compressor. In the compressor having the above described apparatus, the load acting with respect to the motor upon starting of the compressor, is accordingly reduced.
On the other hand, in order to reduce the electrical power consumption, a pressure switch is provided in an air tank of the air compressor, to stop the operation of the compressor when the pressure within the air tank exceeds a predetermined pressure. Moreover, when the pressure within the air tank becomes lower than a predetermined pressure, the compressor is again operated (re-started). In the compressor operated in this manner, in a case where the above manual type starting load reducing apparatus is used in order to reduce the load upon starting of the compressor, the above described manual manipulation must be performed every time the compressor starts another operation, before the starting of the operation or with a same timing as the starting of the operation. However, it is actually impossible to perform the above manual manipulation every time the compressor is started. Therefore, the manual type starting load reducing apparatus cannot be applied to the compressor operated in the above described manner.
Hence, in reality, the air compressor is constructed so that the main compressor body starts the compressing operation from the starting of the air compressor. Furthermore, a motor capable of generating a sufficiently large starting torque which exceeds the large load of the main compressor body, such as a single-phase capacitor-start type motor, is used for the small-size air compressor. However, this capacitor-start type of a motor is high in cost and large in size, and further, the electrical power consumption of this type of a motor is high. Therefore, there was a disadvantage in that the cost and the electrical power consumption of the compressor became high, to increase the operational cost of the compressor.